The couple were clearly too busy to notice boyfriend Mariano coming to sit next to them to catch them on camera.

In the photo the girl is caught red-handed passionately kissing the man as Mariano watches just inches away.

He uploaded the shot to social media with the caption: "My girlfriend (now ex) did not realise we came to the same party."

A man took a selfie of the moment his cheating girlfriend passionately kissed another guy at a party

The unnamed girlfriend reportedly did not find out that Mariano had seen her with the other man until she saw it online.

After the photo spread across social media, receiving over 67,300 likes, Mariano, from Quilmes in the Argentinian state of Buenos Aires, posted a screenshot of his girlfriend's apparent explanation of the incident.

In the messages, the girl said: "I was very drunk and the [other man] was very insistent with me, he told me loads of things and I do not know how it came to that.

"I seriously love you and I want to be with you."

Mariano responded with a laughing emoji and the message: "You could have made a bit more of an effort."

The couple are said to have now split up.

This article originally appeared on The Sun and has been published with permission.